Ammonia is the preferred low-cost environmentally friendly refrigerant used for most industrial food processes, cold storage, and pharmaceutical applications. Known commercially available ammonia detectors usually incorporate electrochemical sensor cells.
Currently Electrochemical cells are the most effective approach to monitoring low-level NH3 levels. Cells are costly as they degrade over time requiring frequent replacement and the associated electronics add an additional cost and complexity to the sensor. Additionally, electrochemical cells have a limited life time as the electrolyte eventually dries up and this is accelerated in dry hot environments. Also, applications that have zero oxygen environments can't use most electrochemical cells for NH3 detection as the electrolytes redox reaction requires O2 to be present. The redox reaction within the electrolyte is also non-regenerative causing the constituents to be consumed that eventually cause the cell to stop functioning should a large NH3 exposure occur, or if a small long-term background is present.
Additional applications where most electrochemical technology is not practical occur in chicken houses because of the constant background of NH3 found in urine, live stock indoor air quality control because of the constant background of NH3 in urine, dry/hot conditions. “Zero Oxygen” applications commonly found in fruit cold storage. Fruit storage or any environment requiring oxygen to be displaced using CO2 or N2 filled rooms to delay fruit ripening doesn't allow electrochemical cells to detect ammonia. Solar panel manufacturing also requires some oxygen to be displaced to reduce spontaneous explosions from chemicals used in the manufacturing process.
Another problematic issue with electrochemical cells is the destruction of the electrolyte and the internal electrodes within the cell when exposed to VOC evaporates. A multitude of cleaning and solvent chemicals can destroy the integrity of most electrochemical cells slowing the response to NH3 down or cause the cell to no longer detect NH3. This creates a safety hazard as there would not be sufficient time to warn individuals near the sensor of the presence of NH3 causing a safety hazard should an NH3 leak occur.
Further, NDIR-type detectors that use the popular 3.3 μm band are costly and do not function as well because NH3 has low IR absorption characteristics requiring high-gain sensitive components, highly polished surfaces, long path lengths, and complex precision optics. Ammonia has a very low absorption characteristic at this wavelength. In general, NDIR detectors are not as practical in ammonia gas detectors at the 3.3 μm, 10.4 μm, or 10.75 μm bands because the absorption bands very narrow, making it difficult to achieve stable signal levels for accurate detection readings near the 0-100 ppm range as the zero has a tendency to drift over time with this type of sensing technology. In addition, water vapor has IR absorption throughout the ammonia absorption spectra diluting signal levels and causing false alarms in wet humid environments. In a photo-acoustic system, the “zero” occurs naturally with no analyte present requiring minimal baseline signal correction compared to NDIR systems.